The Collaborative International Dictionary of English v.0.48:

Whistle \Whis"tle\, v. i. [imp. & p. p. Whistled; p. pr. & vb.
   n. Whistling.] [AS. hwistlian; akin to Sw. hvissla, Dan.
   hvisle, Icel. hv[imac]sla to whisper, and E. whisper.
   [root]43. See Whisper.]
   [1913 Webster]
   1. To make a kind of musical sound, or series of sounds, by
      forcing the breath through a small orifice formed by
      contracting the lips; also, to emit a similar sound, or
      series of notes, from the mouth or beak, as birds.
      [1913 Webster]

            The weary plowman leaves the task of day,
            And, trudging homeward, whistles on the way. --Gay.
      [1913 Webster]

   2. To make a shrill sound with a wind or steam instrument,
      somewhat like that made with the lips; to blow a sharp,
      shrill tone.
      [1913 Webster]

   3. To sound shrill, or like a pipe; to make a sharp, shrill
      sound; as, a bullet whistles through the air.
      [1913 Webster]

            The wild winds whistle, and the billows roar.
                                                  --Pope.
      [1913 Webster]